The Sky is Falling: Meteors and Meteorites Through History

Meteoritics is the branch of science that deals with meteoroids, meteors, and meteorites. Meteoroids are objects travelling in space that range from tiny dust particles to small asteroids. A meteor is a meteoroid that enters the Earth’s atmosphere and burns up due to friction, producing a shooting star or a fireball (as in the artistic rendition shown here). The rocky and metallic fragments that hit the Earth’s surface are called meteorites. The understanding of these phenomena took centuries to evolve, and counted on our intrinsic human curiosity about the sky above and how we are connected with it. 

This 17th century engraving illustrates the way the Ancient Greek philosopher, Aristotle, conceptualized the cosmos. The immobile Earth is surrounded by moving spheres that carry the Moon, the Sun, the planets, and the stars. According to Aristotle, below the Moon’s sphere everything is made out of four elements: earth, water, air, and fire. The heavens beyond are made of a fifth element, the ether, and are perfect and immutable. In this conception, it was inconceivable that phenomena such as meteors, fireballs, or comets could actually originate in space, therefore they were regarded as atmospheric events. 

This photograph shows visitors looking at a meteorite in the Adler Planetarium, which is home to a small but significant collection of meteorites. Meteorite collections started to be assembled by scholars and amateurs from the late 18th century onwards. These collections allow for the systematic and comparative study of meteorites of different types and origins. By the turn of the 19th century, the comparative analysis of the various meteorite samples led scientists to accept that they could have an originated outside of the Earth. 

The solar system is shown in this 19th-century illustration with the few asteroids that were known to exist by the mid-1850s. The first one was discovered in 1801; by the end of the 19th-century, more than 500 had been found, and the number kept on growing (the count is now over 800,000). The illustration also shows the orbit of a comet. During the 1800s, a consensus developed around the idea that meteorites originated from different parent bodies, and that most of them came from asteroids, comets, or interstellar space. 

Meteor showers such as the Perseids (in which meteors radiate from the constellation of Perseus) and the Leonids happen every year, in August and November respectively. The number of observed meteors per hour varies from year to year. In the 1860s, the Italian astronomer Giovanni Schiaparelli found a connection between the orbits of comets and meteor showers, concluding that these events take place when the Earth crosses the trail of dust and particles left by a certain comet in its passage through the inner solar system. Those particles burn up when they enter the Earth’s atmosphere, resulting in swarms of meteors. Schiaparelli ascribed the Perseids to the comet Swift-Tuttle, and the Leonids to the comet Tempel-Tuttle. 

Amateurs have also played an important role in  advancing our knowledge about meteorites and their influence on Earth’s history. Such was the case of Harvey H. Nininger, a self-taught meteorite researcher and collector. Nininger was a keen promoter of the idea that what is now known as the Meteor Crater in Arizona, shown here, resulted from a meteoritic impact. The idea was initially met with resistance, but it is now accepted that the crater resulted from an impact of a 40- to 50-meter iron-nickel asteroid some 50,000 years ago. Nininger’s large meteorite collection is now split by a few institutions, including the Adler Planetarium, which houses roughly 70 meteorites that were originally gathered by this amateur researcher.  

Adler’s meteorite collection includes meteorites from asteroids, the Moon, and even Mars. Studying the composition of meteorites like these gives astronomers information about how objects in our solar system formed and evolved. For example, one of our Martian meteorites is about 200 million years old and is composed of rock that formed from cooling magma, which gives clues to the history of geologic activity on the red planet. Some meteorites contain chondrules, small pieces of material that date back to the formation of our solar system 4.56 billion years ago. Getting to hold a piece of this history in your hands, whether it’s a rock from the moon, from Mars, or from our early solar system, is an exciting opportunity for scientists and Adler guests alike.